A turbine typically includes a plurality of turbine stages arranged in series. Each stage often includes a rotating component and a stationary component. Energy is extracted from the gas flow path in each of these stages, and is converted into rotational energy of the rotating component, leading to a pressure drop across each of the individual stages. This pressure drop across each of the individual stages gives rise to a net thrust within the turbine. It is often desirable to balance the thrust produced in order to reduce the mechanical stresses on the turbine.
Moreover, the extraction of the energy from the various stages is accompanied by losses in each of the individual stages, individual casings and the entire turbine. For example, in a casing associated with a high pressure (HP) stage of a turbine, losses may occur in the form of end and inter-stage leakages. Leakages may be gas flows, such as steam flows, that bypass either stationary or rotating turbine components. Leakage flows include, for example, flows through leakage control devices such as inter stage packings or end packings, tip spills, and leakages past expansion joints, stationary blade carrier seals or leakages along horizontal joints. The leakage flows reduce the amount of flow in the steam path, leading to a reduction in the amount of work done by the flow, in turn affecting the performance of the turbine.
The leakage flows often lead to degradations in turbine performance. Attempts have been made to reduce or minimize the leakage flows within a turbine. For example, attempts have been made to minimize the leakage passage by minimizing the packing seal diameter and/or the clearances between the rotating and the stationary components of the turbine in the different stages of the turbine. While these attempts may result in a decrease in the leakage flows, a relatively significant leakage flow may remain in the turbine.
Accordingly, there is a need for methods, systems and apparatus for controlling gas leakage in a turbine.